The present invention relates to a disc brake, in particular for a commercial vehicle having a brake caliper and a brake disc, which brake disc can be placed in active contact with brake pads. The caliper is fastened to a brake carrier so as to be axially displaceable relative to the brake disc, for which purpose guide pins are fixedly connected to the brake carrier. The brake caliper is guided on the guide pins, wherein each guide pin is enclosed, in the region formed between the brake caliper and the brake carrier, by a bellows which is fixed at both sides.
In disc brakes of the above-mentioned type, the brake caliper is connected to the brake carrier, which is connected to the vehicle, by way of fastening elements which have guide pins. Here, the guide pins engage at one side in the brake carrier, while at the other side, they are guided in sliding bearings of the brake caliper in such a way that an axial displacement of the brake caliper is possible on the positionally fixed brake carrier.
To protect the guide pins, in particular to prevent dirt accumulation, the associated guide pin is enclosed by a bellows in the respective region between the brake carrier and the brake caliper. On account, predominantly, of a lack of space, the bellows is dimensioned to be as small as possible, so that it bears closely against the guide pin, wherein the peripheral head regions of the folds which face toward the guide pin function practically as sealing lips, producing hermetically sealed-off chambers in each case as a result.
During a slow movement of the brake caliper, as occurs during re-adjustment of the brake carrier on account of wear, the quantity of air enclosed in the bellows is equalized corresponding to the change in volume by way of diffusion, that is to say air molecules permeate through the wall of the bellows in one or the other direction, so that no high pressure or vacuum results in the chambers which are formed. Here, the number of folds and their height are dependent on the working stroke which is to be performed by the disc brake.
When the brake caliper is displaced away from the brake carrier, the bellows adheres to the bar as a result of the vacuum which is produced, wherein the close-fitting peripheral head regions, which undesirably form sealing lips, of the folds which face toward the guide pin form vacuum chambers, which are independent of one another.
When the brake caliper is displaced in the opposite direction, that is to say toward the brake carrier, the vacuum formed in the first chamber which faces toward the brake caliper is reduced as a result of the displacement, wherein the fold is relieved of load and the bellows can fold together again in that region. The subsequent chambers, in contrast, remain adhered as a result of the vacuum, and are no longer folded. As a result, during the continued axial displacement of the brake caliper, the bellows is, so to speak, folded around and is pulled into the guide bore of the brake caliper, so that, in some circumstances, the bellows is damaged, which can lead to failure of the brake.
The present invention is, therefore, based on the object of further developing a disc brake of the above-mentioned type such that, using structurally simple means, function-related damage to the bellows is eliminated, and the operational reliability of the disc brake is improved overall.
This and other objects are achieved by providing a disc brake having a brake caliper and a brake disc, which brake disc can be placed in active contact with brake pads. The caliper is fastened to a brake carrier so as to be axially displaceable relative to the brake disc, for which purpose guide pins are fixedly connected to the brake carrier. The brake caliper is guided on the guide pins, wherein each guide pin is enclosed, in the region formed between the brake caliper and the brake carrier, by a bellows which is fixed at both sides. The peripheral head regions of those folds of the bellows, which face toward the guide pin, have a circumferential contour which is different to the circumference of the guide pin.
The modification to the bellows, which is additionally possible with little additional production expenditure, actively prevents the possibility of a vacuum, as a result of which the wall of the bellows would bear largely with its entire surface against the guide pin, not being produced in the separately formed chambers.
In addition, there is pressure equalization between the individual chambers, so that the bellows can permanently perform its intended function in an unrestricted fashion.
A displacement of the brake caliper in the direction of the brake carrier leads to a reduction of the vacuum not only in the first chamber, which is adjacent to the brake caliper, but rather in the entire space enclosed by the bellows. This ensures that the bellows folds uniformly in a functional manner, so that it is prevented from being damaged as described with regard to the prior art.
As a result of the circumferential contour of the head regions of the fold, which face toward the guide pin, being different from the preferably circular circumference of the guide pin, gap formation is partially obtained. As a result, a one-chamber system is practically formed with regard to pressure equalization and/or the exchange of air. This prevents the formation of sealing lips which bear against the guide pin in a continuous fashion.
According to an advantageous refinement of the invention, it is provided that the corresponding peripheral head region of each fold is provided with at least one knob, which bears against the guide pin and additionally spaces the folds apart from the guide pin while forming a gap. Here, pressure equalization is obtained by way of the gap which is formed.
The pressure equalization may also be obtained if, instead of the knob, which constitutes a positive formation, a comparable cut-out, which in contrast forms a negative formation, is provided in the head region of the respective fold. The cut-out provides a flow passage between two adjacent chambers.
If required, a plurality of knobs or cut-outs may also be provided more or less uniformly over the circumference.
Another circumferential contour, which is different from the circumferential contour of the guide pin, of the head regions of the folds is also templated, for example in the form of a polygon, in which the sides of the polygon bear against the guide pin, while the formed corner region provide the desired passage.
The same effect is obtained with an oval contouring, which likewise leads to gap formation relative to the round circular contour of the guide pin, specifically at two opposite end regions, wherein it is sufficient for the greatest dimension of the contour of the head region to be kept slightly larger than the smallest dimension, which is associated with the head region and by way of which the corresponding fold bears against the guide pin.
It is to be noted in any case that those head regions of the bellows which are associated with the guide pin do not bear completely against the outer face of the guide pin during deformation.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.